Safety of heterologous ChAdOx1-S/BNT162b2 primary schedule versus homologous BNT162b2 vaccination: Insights from an Italian post-marketing study, 2021.

During COVID-19 vaccination campaign, possible ChAdOx1-S-associated risks of thrombosis with thrombocytopenia syndrome led to implement ChAdOx1-S/BNT162b2 heterologous vaccination, despite the limited information on its reactogenicity and safety. We conducted a prospective observational post-marketing surveillance study to assess the safety of this heterologous schedule. A casually selected sample of recipients (n: 85; age: 18-60 years) of ChAdOx1-S/BNT162b2 at the vaccination hub of the Foggia Hospital, Italy, was matched with an equal sample of recipients of homologous BNT162b2. Safety was evaluated 7 days, 1 month and 14 weeks after the primary vaccination series using an adapted version of the "V-safe active surveillance for COVID-19 vaccine safety" CDC standardized questionnaire. After 7 days, local reactions were highly frequent (>80%) in both groups, and systemic reactions were less common (<70%). Moderate or severe pain at the injection site (OR = 3.62; 95%CI, 1.45-9.33), moderate/severe fatigue (OR = 3.40; 95%CI, 1.22-9.49), moderate/severe headache (OR = 4.72; 95%CI, 1.37-16.23), intake of antipyretics (OR = 3.05; 95 CI%, 1.35-6.88), inability to perform daily activities and work (OR = 2.64; 95%CI, 1.24-5.62) were significantly more common with heterologous than homologous vaccination. No significant difference in self-reported health status was recorded 1 month or 14 weeks after the second dose with BNT162b2 or ChAdOx1-S/BNT162b2. Our study confirms the safety of both heterologous and homologous vaccination, with a slight increase in some short-term adverse events for the heterologous regimen. Therefore, administering a second dose of a mRNA vaccine to the recipients of a previous dose of viral vector vaccine may have represented an advantageous strategy to improve flexibility and to accelerate the vaccination campaign.

Corrigendum: The impact of circadian rhythm on Bacillus Calmette-Guérin vaccination effects on SARS-CoV-2 infections.

[This corrects the article DOI: 10.3389/fimmu.2023.980711.].

Heterologous prime boost COVID 19 vaccination.

Heterologous prime boost vaccination is a primary vaccination with different vaccines, most often from different vaccine platforms. It combines the immunological properties of the different vaccines and thereby induces humoral, cellular and, in some cases, mucosal response. For Covid prevention, it has been used in primary vaccination, due to safety issues and in boosters. We have evaluated some articles reporting on the results of this type of vaccine, and demonstrating its usefulness.

Intravenous heterologous prime-boost vaccination activates innate and adaptive immunity to promote tumor regression.

Therapeutic neoantigen cancer vaccines have limited clinical efficacy to date. Here, we identify a heterologous prime-boost vaccination strategy using a self-assembling peptide nanoparticle TLR-7/8 agonist (SNP) vaccine prime and a chimp adenovirus (ChAdOx1) vaccine boost that elicits potent CD8 T cells and tumor regression. ChAdOx1 administered intravenously (i.v.) had 4-fold higher antigen-specific CD8 T cell responses than mice boosted by the intramuscular (i.m.) route. In the therapeutic MC38 tumor model, i.v. heterologous prime-boost vaccination enhances regression compared with ChAdOx1 alone. Remarkably, i.v. boosting with a ChAdOx1 vector encoding an irrelevant antigen also mediates tumor regression, which is dependent on type I IFN signaling. Single-cell RNA sequencing of the tumor myeloid compartment shows that i.v. ChAdOx1 reduces the frequency of immunosuppressive Chil3 monocytes and activates cross-presenting type 1 conventional dendritic cells (cDC1s). The dual effect of i.v. ChAdOx1 vaccination enhancing CD8 T cells and modulating the TME represents a translatable paradigm for enhancing anti-tumor immunity in humans.

Comparing Heterologous and Homologous COVID-19 Vaccination: A Longitudinal Study of Antibody Decay.

The humoral response after vaccination was evaluated in 1248 individuals who received different COVID-19 vaccine schedules. The study compared subjects primed with adenoviral ChAdOx1-S (ChAd) and boosted with BNT162b2 (BNT) mRNA vaccines (ChAd/BNT) to homologous dosing with BNT/BNT or ChAd/ChAd vaccines. Serum samples were collected at two, four and six months after vaccination, and anti-Spike IgG responses were determined. The heterologous vaccination induced a more robust immune response than the two homologous vaccinations. ChAd/BNT induced a stronger immune response than ChAd/ChAd at all time points, whereas the differences between ChAd/BNT and BNT/BNT decreased over time and were not significant at six months. Furthermore, the kinetic parameters associated with IgG decay were estimated by applying a first-order kinetics equation. ChAd/BNT vaccination was associated with the longest time of anti-S IgG negativization and with a slow decay of the titer over time. Finally, analyzing factors influencing the immune response by ANCOVA analysis, it was found that the vaccine schedule had a significant impact on both the IgG titer and kinetic parameters, and having a Body Mass Index (BMI) above the overweight threshold was associated with an impaired immune response. Overall, the heterologous ChAd/BNT vaccination may offer longer-lasting protection against SARS-CoV-2 than homologous vaccination strategies.

Long-Term Cross Immune Response in Mice following Heterologous Prime-Boost COVID-19 Vaccination with Full-Length Spike mRNA and Recombinant S1 Protein.

(1) Background: As the COVID-19 pandemic enters its fourth year, it continues to cause significant morbidity and mortality worldwide. Although various vaccines have been approved and the use of homologous or heterologous boost doses is widely promoted, the impact of vaccine antigen basis, forms, dosages, and administration routes on the duration and spectrum of vaccine-induced immunity against variants remains incompletely understood. (2) Methods: In this study, we investigated the effects of combining a full-length spike mRNA vaccine with a recombinant S1 protein vaccine, using intradermal/intramuscular, homologous/heterologous, and high/low dosage immunization strategies. (3) Results: Over a period of seven months, vaccination with a mutant recombinant S1 protein vaccine based on the full-length spike mRNA vaccine maintained a broadly stable humoral immunity against the wild-type strain, a partially attenuated but broader-spectrum immunity against variant strains, and a comparable level of cellular immunity across all tested strains. Furthermore, intradermal vaccination enhanced the heterologous boosting of the protein vaccine based on the mRNA vaccine. (4) Conclusions: This study provides valuable insights into optimizing vaccination strategies to address the ongoing challenges posed by emerging SARS-CoV-2 variants.

Immunogenicity and safety of heterologous mRNA-1273/MVC-COV1901 vaccination versus homologous mRNA1273 vaccination: A randomized, double-blind controlled study.

BACKGROUND/PURPOSE: MVC-COV1901 is a protein vaccine based on the same SARS-CoV-2 strain used in mRNA vaccine mRNA-1273. Data are lacking on immunogenicity and safety of MVC-COV1901 as heterologous boost for people already received one dose of mRNA-1273. METHODS: This is a randomized, double-blind trial that recruited adults aged 20-70 years who previously received a single dose of mRNA-1273 vaccine and were randomly assigned in a 1:1 ratio to receive a second dose with the homologous vaccine or protein-based MVC-COV1901 8-12 weeks after the first dose. The primary outcome was neutralizing antibody titers in terms of the geometric mean titer (GMT) 14 days after the second dose. Safety was assessed in all participants who received a dose of the study vaccine. The study is registered with ClinicalTrials.gov (NCT05079633). RESULTS: From September 30 to November 5, 2021, 144 participants were enrolled and randomly assigned to the MVC-COV1901 boost group (n = 72) or the mRNA-1273 boost group (n = 72). The neutralizing antibodies on Day 15 and the anti-SARS-CoV-2 IgG titers on Day 15 and 29 of homologous mRNA-1273 were significantly higher than those of heterologous mRNA-1273/MVC-COV1901. Cellular immune responses were comparable in both groups. However, adverse events were much more frequent after the mRNA-1273 boost than after the MVC-COV1901 boost. CONCLUSION: Our results show that heterologous boost with MVC-COV1901 yielded an inferior immunogenicity but significantly fewer adverse events, compared with homologous boost with mRNA-1273. In people experienced severe adverse events after prime dose of mRNA-1273, as well as in periods when the supply of mRNA-1273 is limited, MVC-COV1901 could serve as an acceptable alternative heterologous boost.

Humoral Response after a Fourth Dose with mRNA-1273 in Healthcare Workers with and without a History of SARS-CoV-2 Infection and Previously Vaccinated with Two Doses of BBIBP-CorV Plus BNT162b2 Vaccine.

There is limited information on the kinetics of the humoral response elicited by a fourth dose with a heterologous mRNA1273 booster in patients who previously received a third dose with BNT162b2 and two doses of BBIBP-CorV as the primary regimen. We conducted a prospective cohort study to assess the humoral response using Elecsys® anti-SARS-CoV-2 S (anti-S-RBD) of 452 healthcare workers (HCWs) in a private laboratory in Lima, Peru at 21, 120, 210, and 300 days after a third dose with a BNT162b2 heterologous booster in HCW previously immunized with two doses of BBIBP-CorV, depending on whether or not they received a fourth dose with the mRNA1273 heterologous vaccine and on the history of previous SARS infection -CoV-2. Of the 452 HCWs, 204 (45.13%) were previously infected (PI) with SARS-CoV-2, and 215 (47.57%) received a fourth dose with a heterologous mRNA-1273 booster. A total of 100% of HCWs presented positive anti-S-RBD 300 days after the third dose. In HCWs receiving a fourth dose, GMTs 2.3 and 1.6 times higher than controls were observed 30 and 120 days after the fourth dose. No statistically significant differences in anti-S-RBD titers were observed in those HCWs PI and NPI during the follow-up period. We observed that HCWs who received a fourth dose with the mRNA1273 and those previously infected after the third dose with BNT162b2 (during the Omicron wave) presented higher anti-S-RBD titers (5734 and 3428 U/mL, respectively). Further studies are required to determine whether patients infected after the third dose need a fourth dose.

Assessment of Anti-SARS-CoV-2 antibody levels among university students vaccinated with different COVID-19 primary and booster doses - fall 2021, Wisconsin.

BACKGROUND: University students commonly received COVID-19 vaccinations before returning to U.S. campuses in the Fall of 2021. Given likely immunologic variation among students based on differences in type of primary series and/or booster dose vaccine received, we conducted serologic investigations in September and December 2021 on a large university campus in Wisconsin to assess anti-SARS-CoV-2 antibody levels. METHODS: We collected blood samples, demographic information, and COVID-19 illness and vaccination history from a convenience sample of students. Sera were analyzed for both anti-spike (anti-S) and anti-nucleocapsid (anti-N) antibody levels using World Health Organization standardized binding antibody units per milliliter (BAU/mL). Levels were compared across categorical primary COVID-19 vaccine series received and binary COVID-19 mRNA booster status. The association between anti-S levels and time since most recent vaccination dose was estimated by mixed-effects linear regression. RESULTS: In total, 356 students participated, of whom 219 (61.5%) had received a primary vaccine series of Pfizer-BioNTech or Moderna mRNA vaccines and 85 (23.9%) had received vaccines from Sinovac or Sinopharm. Median anti-S levels were significantly higher for mRNA primary vaccine series recipients (2.90 and 2.86 log [BAU/mL], respectively), compared with those who received Sinopharm or Sinovac vaccines (1.63 and 1.95 log [BAU/mL], respectively). Sinopharm and Sinovac vaccine recipients were associated with a significantly faster anti-S decline over time, compared with mRNA vaccine recipients (P <.001). By December, 48/172 (27.9%) participants reported receiving an mRNA COVID-19 vaccine booster, which reduced the anti-S antibody discrepancies between primary series vaccine types. CONCLUSIONS: Our work supports the benefit of heterologous boosting against COVID-19. COVID-19 mRNA vaccine booster doses were associated with increases in anti-SARS-CoV-2 antibody levels; following an mRNA booster dose, students with both mRNA and non-mRNA primary series receipt were associated with comparable levels of anti-S IgG.

Heterologous vaccination with inactivated vaccine and mRNA vaccine augments antibodies against both spike and nucleocapsid proteins of SARS-CoV-2: a local study in Macao.

The mRNA vaccines (RVs) can reduce the severity and mortality of severe acute respiratory syndrome coronavirus (SARS-CoV-2). However, almost only the inactivated vaccines (IVs) but no RVs had been used in mainland China until most recently, and the relaxing of its anti-pandemic strategies in December 2022 increased concerns about new outbreaks. In comparison, many of the citizens in Macao Special Administrative Region of China received three doses of IV (3IV) or RV (3RV), or 2 doses of IV plus one booster of RV (2IV+1RV). By the end of 2022, we recruited 147 participants with various vaccinations in Macao and detected antibodies (Abs) against the spike (S) protein and nucleocapsid (N) protein of the virus as well as neutralizing antibodies (NAb) in their serum. We observed that the level of anti-S Ab or NAb was similarly high with both 3RV and 2IV+1RV but lower with 3IV. In contrast, the level of anti-N Ab was the highest with 3IV like that in convalescents, intermediate with 2IV+1RV, and the lowest with 3RV. Whereas no significant differences in the basal levels of cytokines related to T-cell activation were observed among the various vaccination groups before and after the boosters. No vaccinees reported severe adverse events. Since Macao took one of the most stringent non-pharmaceutical interventions in the world, this study possesses much higher confidence in the vaccination results than many other studies from highly infected regions. Our findings suggest that the heterologous vaccination 2IV+1RV outperforms the homologous vaccinations 3IV and 3RV as it induces not only anti-S Ab (to the level as with 3RV) but also anti-N antibodies (via the IV). It combines the advantages of both RV (to block the viral entry) and IV (to also intervene the subsequent pathological processes such as intracellular viral replication and interference with the signal transduction and hence the biological functions of host cells).

A case report overlapped vaccine and COVID-19 in disseminated atherosclerosis.

Coronavirus disease 2019 (COVID-19) has become a part of our lives now and we have no more effective way of coping than a vaccine. COVID-19 is a disease that causes severe thrombosis outside the respiratory tract. Vaccines also protect us in this respect, but in some rare cases, thrombosis has been found to develop after vaccination (much less frequently than COVID-19). What was interesting in our case was that it showed how a disaster could happen under three factors that predispose to thrombosis. A 65-year-old female patient with disseminated atherosclerosis was admitted to the intensive care unit with complaints of dyspnea and dysphasia. In the evening of the day, the patient had the vaccination 2 weeks ago, she had active COVID-19. On examination, lower extremity pulses could not be detected. The patient's imaging and blood tests were performed. Multiple complications such as embolic stroke, venous and arterial thrombosis, pulmonary embolism, and pericarditis were observed in the patient. This case may give consideration to anticoagulant therapy studies. We give effective anticoagulant therapy in the presence of COVID-19 in patients at risk of thrombosis. Can anticoagulant therapy be considered after vaccination in patients at risk of thrombosis such as disseminated atherosclerosis?

Omicron infection-associated T- and B-cell immunity in antigen-naive and triple-COVID-19-vaccinated individuals.

Since early 2022, various Omicron variants have dominated the SARS-CoV-2 pandemic in most countries. All Omicron variants are B-cell immune escape variants, and antibodies induced by first-generation COVID-19 vaccines or by infection with earlier SARS-CoV-2 variants largely fail to protect individuals from Omicron infection. In the present study, we investigated the effect of Omicron infections in triple-vaccinated and in antigen-naive individuals. We show that Omicron breakthrough infections occurring 2-3.5 months after the third vaccination restore B-cell and T-cell immune responses to levels similar to or higher than those measured 14 days after the third vaccination, including the induction of Omicron-neutralizing antibodies. Antibody responses in breakthrough infection derived mostly from cross-reacting B cells, initially induced by vaccination, whereas Omicron infections in antigen-naive individuals primarily generated B cells binding to the Omicron but not the Wuhan spike protein. Although antigen-naive individuals mounted considerable T-cell responses after infection, B-cell responses were low, and neutralizing antibodies were frequently below the limit of detection. In summary, the detection of Omicron-associated B-cell responses in primed and in antigen-naive individuals supports the application of Omicron-adapted COVID-19 vaccines, but calls into question their suitability if they also contain/encode antigens of the original Wuhan virus.

COVID-19: Delphi analysis for the evaluation of the transition from pandemic to endemic in Mexico.

OBJECTIVE: To review and analyze the available information about the COVID-19 pandemic in Mexico and the determining factors for its transition to an endemic phase. MATERIALS AND METHODS: Prospective study based on the Delphi Method with the participation of a panel made up by specialists in infectious diseases, immunology, internal medicine, pulmonology, pediatrics and public health. RESULT(S): 2270 bibliographic sources were identified;after excluding those that offered repetitive information, 454 were included in the final analysis. The main factors that obstruct the transition from a COVID-19 pandemic to an endemic one were defined as the high capacity of SARS-CoV-2 to mutate (since the efficacy of anti-COVID-19 vaccines depends to a large extent on the genetic presentations of the virus) and the high prevalence in the country of comorbidities that make the population more vulnerable against the disease. Strengthening primary care and promoting a culture of surveillance and prevention are essential. CONCLUSION(S): It was concluded, by consensus, that there are factors that obstruct the passage of the COVID-19 pandemic to an endemic phase, including the intrinsic nature of disease control and the unpredictability of virus mutations.Copyright © 2023 Comunicaciones Cientificas Mexicanas S.A. de C.V.. All rights reserved.

REACTOGENICITY OF HETEROLOGOUS MRNA-BASED COVID-19 VACCINE BOOSTER IN YOUNG ADULTS IN INDONESIA- A SHORT COMMUNICATION.

Background: Heterologous priming with the inactivated SARS-CoV-2 vaccine (CoronaVac) and boosting with mRNA-based COVID-19 vaccine (Moderna or Pfizer) is currently recommended in Indonesia. The reactogenicity data of these heterologous vaccine regimens are not entirely available, particularly in young adults. The present study, therefore, aimed to evaluate the solicited local and systemic reactions in the first seven days post-vaccination either with Moderna or Pfizer vaccine among previous recipients of two doses of CoronaVac. Materials and Methods: An electronic-based cross-sectional study was conducted among medical students at the Pelita Harapan University, Banten, Indonesia, who received mRNA-based COVID-19 vaccine following two doses of CoronaVac. Samples were collected using a cluster sampling technique. Comparison between groups was performed by Fisher's exact test. Results: A total of 72 participants, 23 (32%) of which received the Moderna vaccine and 49 (68%) received the Pfizer vaccine, were included in this study. The median age of participants was 21 (IQR 19-22) years old. The most common local and systemic events for mRNA-based COVID-19 vaccines were injection site pain, fever, headache, fatigue, myalgia, and arthralgia. Solicited local and systemic reactions were reported more frequently in Moderna recipients than Pfizer recipients. Most local and systemic reactions were graded as mild to moderate and did not lead to hospitalization. Conclusions: The reactogenicity of the heterologous prime-boost with CoronaVac and mRNA-based COVID-19 vaccine booster among young adults is reassuring, and no unexpected concerns were identified.

Self-reported adverse events after 2 doses of COVID-19 vaccine in Korea.

OBJECTIVES: In Korea, a national coronavirus disease 2019 (COVID-19) vaccination program was implemented, including 4 vaccines against COVID-19. A text messaging-based survey, in addition to a passive adverse event reporting system, was launched to quickly report unusual symptoms post-vaccination. This study compared the frequency of adverse events after COVID-19 vaccination based on the vaccine type and the type of 2-dose regimen (homologous or heterologous). METHODS: Self-reported adverse events were collected through a text-message survey for 7 days after each vaccination. This study included 50,950 vaccine recipients who responded to the survey at least once. Informed consent to receive surveys via text was obtained from the vaccine recipients on the date of first vaccination. RESULTS: The recipients of mRNA vaccines reported local and systemic reactions 1.6 times to 2.8 times more frequently after dose 2 than after dose 1 (p<0.001), whereas ChAdOx1-S recipients reported significantly fewer local and systemic reactions after dose 2 than after dose 1 (p<0.001). Local and systemic reactions were approximately 2 times and 4 times more frequent for heterologous vaccination than for BNT162b2/BNT162b2 and ChAdOx1-S/ChAdOx1-S regimens, respectively. Young individuals, female, and those receiving heterologous vaccine regimens including ChAdOx1-S/BNT162b2 vaccines reported more adverse events than older participants, male, and those with homologous vaccine regimens. CONCLUSIONS: Although a heterologous regimen, youth, and female sex were associated with a higher risk of adverse reactions after COVID-19 vaccination, no critical issues were noted. Active consideration of heterologous schedules based on the evidence of efficacy and safety appears desirable.

Immunogenicity and safety of a single booster dose of NVX-CoV2373 (TAK-019) in healthy Japanese adults who had previously received a primary series of COVID-19 mRNA vaccine: Primary analysis report of a phase 3 open-label trial.

BACKGROUND: We evaluated the immunogenicity and safety of a booster dose of NVX-CoV2373 in Japanese adults who had completed a primary series of COVID-19 mRNA vaccine 6-12 months previously. METHODS: This single-arm, open-label, phase 3 study, conducted at two Japanese centres, enrolled healthy adults ≥ 20 years old. Participants received a booster dose of NVX-CoV2373. The primary immunogenicity endpoint was non-inferiority (lower limit of the 95 % confidence interval [CI] ≥ 0.67) of the geometric mean titre (GMT) ratio of titres of serum neutralizing antibodies (nAbs) against the SARS-CoV-2 ancestral strain 14 days after booster vaccination (day 15) in this study, compared with those 14 days after the second primary NVX-CoV2373 vaccination (day 36) in the TAK-019-1501 study (NCT04712110). Primary safety endpoints included local and systemic solicited adverse events (AEs) up to day 7 and unsolicited AEs up to day 28. RESULTS: Between 15 April 2022 and 10 May 2022, 155 participants were screened and 150, stratified by age (20-64 years old [n = 135] or ≥ 65 years old [n = 15]), received an NVX-CoV2373 booster dose. The GMT ratio between titres of serum nAbs against the SARS-CoV-2 ancestral strain on day 15 in this study and those on day 36 in the TAK-019-1501 study was 1.18 (95 % CI, 0.95-1.47), meeting the non-inferiority criterion. Following vaccination, the proportion of participants who reported local and systemic solicited AEs up to day 7 was 74.0 % and 48.0 %, respectively. The most common local and systemic solicited AEs were tenderness (102 participants [68.0 %]) and malaise (39 participants [26.0 %]), respectively. Seven participants (4.7 %) reported unsolicited AEs between vaccination and day 28; all were severity grade ≤ 2. DISCUSSION: A single heterologous NVX-CoV2373 booster induced rapid and robust anti-SARS-CoV-2 immune responses, addressing waning immunity in healthy Japanese adults, and had an acceptable safety profile. CLINICALTRIALS: gov identifier: NCT05299359.

Immunogenicity and reactogenicity of heterologous prime-boost vaccination with inactivated COVID-19 and ChAdOx1 nCoV-19 (AZD1222) vaccines, a quasi-experimental study.

The global supply of COVID-19 vaccines has been limited, and concerns have arisen about vaccine supply chain disruptions in developing countries. Heterologous prime-boost vaccination, which involves using different vaccines for the first and second doses, has been proposed to enhance the immune response. We aimed to compare the immunogenicity and safety of a heterologous prime-boost vaccination using an inactivated COVID-19 vaccine and AZD1222 vaccine with that of a homologous vaccination using AZD1222. This pilot involved 164 healthy volunteers without prior SARS-CoV-2 infection aged 18 years or older assigned to receive either the heterologous or homologous vaccination. The results showed that the heterologous approach was safe and well-tolerated, although the reactogenicity of the heterologous approach was higher. At 4 weeks after receiving the booster dose, the heterologous approach elicited a non-inferior immune response compared to the homologous approach in neutralizing antibody and cell-mediated immune response. The percentage of inhibition was 83.88 (79.72-88.03) in the heterologous and 79.88 (75.50-84.25) in the homologous group, a mean difference of 4.60 (-1.67-10.88). The geometric mean of interferon-gamma was 1072.53 mIU/mL (799.29-1439.18) in the heterologous group and 867.67 mIU/mL (671.94-1120.40) in the homologous group, a GMR of 1.24 (0.82-1.85). However, the binding antibody test of the heterologous group was inferior to the homologous group. Our findings suggest that the use of heterologous prime-boost vaccination with different types of COVID-19 vaccines is a viable strategy, especially in settings where vaccine supply is limited or where vaccine distribution is challenging.

Evaluation of Side Effects After Heterologous Vaccination with BNT162b2 Vaccine in Healthcare Workers Vaccinated with Two Doses of Inactive COVID-19 Vaccine

Objective: Vaccination is the most effective way to control the COVID-19 pandemic all over the world. We aimed to evaluate the relationship between antibody titers and vaccine side effects after the BNT162b2 vaccine was administered as a reminder dose in healthcare workers (HCW) who received two doses of inactivated SARS-CoV-2 vaccine name CoronaVac (Sinovac Life Sciences, Beijing, China).Methods: A total of 428 HCWs participated in the study. Participants who received the mRNA vaccine as a reminder dose were evaluated with a questionnaire regarding antibody values and vaccine side effects. Three weeks after the first BNT162b2 vaccine, the same questionnaire was applied face-to-face to HCW, and the same questionnaire was applied to those who received a second reminder dose via telephone.Results: Out of 428, 373 (87.1%) HCWs preferred one and 55 (12.9%) two doses of the BNT162b2 vaccine as reminder doses after being vaccinated with an inactivated vaccine. It was observed that side effects were more frequent in women aged 18-40 after a single dose of the BNT162b2 vaccine (p<0.001). The most common side effects are redness, swelling, and pain at the injection site, with a rate of 59.6%. Fatigue-weakness was the most common systemic reaction, with a rate of 58.6%. Axillary lymphadenopathy was observed seen in 3 (1.1%) HCWs. The median value of IgG titers in the third week after the reminder dose was found to be higher in HCW with side effects than those without side effects (p<0.001). When the cumulative incidence rate of vaccinated people was evaluated over 389 people, no cases were ob-served on the 14th and 30th days after the first reminder dose of BNT162b2. However, the first case was observed on the 60th day, and after the second reminder dose, cases were seen on the 14th, 30th, and 60th days.Conclusion: Since the side effects detected after the BNT162b2 reminder dose were mild to moderate and progressed with local symptoms, it was concluded that highly protective mRNA vaccines could be safely preferred for protection from COVID-19.

BOOSTER VACCINATION AGAINST SARS-CoV-2: CURRENT CHALLENGES AND SOLUTIONS.

The COVID-19 pandemic is going on, which makes it crucial to prevent the spread of coronavirus disease. Vaccination is the only way of specific prevention of COVID-19. The SARS-CoV-2 virus is continuously evolving and new variants appear. Moreover, the effectiveness of protective immunity after vaccination tends to decrease over several months. Booster vaccination may be the solution to these problems. The booster is an extra vaccination that helps to reactivate the immunity against COVID-19. Booster doses can be homologous (the same as the primary vaccine) and heterologous (different from the primary vaccine). It is of current interest to study heterologous vaccination as the injection of different vaccines may result in a more intense immune response. Furthermore, the same vaccine may not be available at the time of booster vaccination. This review is aimed at summarizing the key research findings in the field of booster vaccination against COVID-19.Copyright © 2022 Booster vaccination against. All rights reserved.