Covid-19 Vaccines: What We Know So Far!
(By Dr Vipin M. Vashishtha, MD)
1-Ten different Covid-19 vaccines have shared their Phase III data; 2 based on mRNA, 4 on viral vector, 3 on inactivated & 1 on protein subunit platform
2-After 4 months of their trials, now there is a definite gradient in their performance:
Highly efficacious: mRNA, moderate: viral vector, &
low to moderate: inactivated vaccines.
3- Efficacy (Point estimates as per published/shared data): Pfizer 95%; Moderna 94.1%, Sputnik-V 91.6%, Novavax 89.3%, AstraZeneca (AZ) 62-90%, Sinopharm’s (BBIBP-CorV) 79%, Covaxin 78%, JNJ 72%, CanSino’s 65.7%, & Sinovac’s (CoronaVac) 50.4%.
4-Quality of evidence (confidence):
• Highest (Real world use, Effectiveness data & Publication of Efficacy trial)-Pfizer, AstraZeneca & Moderna;
• Moderate (Real world use, Publication of efficacy trial): JNJ, Sputnik-V, Sinopharm, & Novavax;
• Low-moderate (Real world data, no publication of efficacy trial): CanSino, Sinovac & Covaxin
5-Israel, Chile, Bahrein, US & UK are the 5 leading countries as far as highest share of fully vaccinated population is concerned
6-Pfizer & AZ vaccines have shown real world effectiveness & population level impact. Though some level of confounding effects of non-pharmaceutical interventions was also present!
7-Sinovac’s CoronaVac vaccine fared poorly in Seychelles & Chile
8-Most vaccines have highest efficacy against severe disease & deaths
9-No vaccine is 100% efficacious against SARS-CoV-2 SARS-COV-2 transmission infection (NO STERILIZING IMMUNITY)! Except Pfizer/Modrena vaccines, most vaccines have only modest efficacy against transmission.
10- Breakthrough infections observed with almost all vaccines. Most mild & moderate, deaths are also seen in fully vaccinated (out of 5800 breakthrough cases with mRNA vaccines in the US, 7% hospitalized & 74 died)
11-Most vaccines have comparatively lower efficacy in elderly & comorbidities than in younger and healthy people
12-Most gene-based vaccines (mRNA & Viral vector) have high reactogenicity profile.
13-Adenovirus vector-based vaccines (AZ & JNJ) have rare, serious adverse events called VITT (vaccine induced immune thrombotic thrombocytopenia). Incidence varies from 1 case in 40 000 to 1 in 100 000, but the benefits far outweigh than the risks
14. Efficacy against variants: Most vaccines have only very modest reductions in efficacy against UK’s B117 & Brazil’s P1 variants. Most vaccines have lower efficacy against South Africa’s B1351 variant (containing E484K mutation).
15-AZ vaccine has got only 10% efficacy against B1351 variant, whereas JNJ (57%) & Novavax (49%) had major reductions in efficacy trials. Sputnik-V, Pfizer & Moderna vaccines have reduced neutralization against B1351.
16-Pfizer vaccine has shown intact efficacy against B1351 in Qatar in real world evidence after 2 doses. Nevertheless, most leading vaccines are developing boosters with revised formulation to tackle B1351 variant.
17-So far, natural infection induced protection seems to be more lasting than vaccine induced, particularly in context with non-mRNA vaccines.
18-Only 4 vaccine candidates elicited several folds higher titers of neutralizing antibodies (NAbs) than natural infection (NAbs titers measured in human convalescent serum): Pfizer, Moderna, Novavax & Sputnik-V. However, natural immunity is much more broader.
19- We know now that natural infection provides at least 8 months of protection. Whereas mRNA vaccines are found to provide protection at least for 6 months without any appreciable loss of efficacy. Other vaccines like inactivated & AZ vaccines may provide lesser duration of protection.
20-Natural infection may provide resistance against immune evader variants also since there is immune responses against not only against S protein but against other antigens of the virus. Further, the variants do not have changes in T-cell epitopes.
21. Most vaccines elicit both humoral and T cell immunity. However, viral vector vaccine, particularly AZ vaccine has got particularly good CD8 cell response which kill virus infected cell and ameliorate severity of disease.
22. Those had natural infection can wait for THREE MONTHS for their Covid vaccine shot.
23. In previously infected individuals with anti-spike IgG positive individuals, only ONE DOSE of mRNA vaccine is sufficient!
24. Though no official recommendation from the WHO, still pregnant women can have the vaccine at any stage of pregnancy. Strong data for 3rd trimester with mRNA vaccines
25. No need to avoid becoming pregnant after having the vaccine
26. There is no evidence to suggest that COVID-19 vaccines will affect fertility
27. No known risk in giving COVID-19 vaccines to women who are breastfeeding. Women who are breastfeeding should be encouraged to continue breastfeeding after being vaccinated
28. Several vaccines are now conducting trials for use of Covid vaccines in pediatric population. Pfizer showed 100% efficacy in 12-15 yrs old, Moderna is doing trial in 6mo to 12 yrs (in US) & 5-11 yrs (in Canada), JNJ 12-17 yrs, Sinovac 3-11 yrs & Novavax 12-17 yrs. AZ has paused their trial in 6-17 yrs.
-Dr Vipin M Vashishtha, MD