Why Your Second Dose COVID-19 Vaccine Can Be Extended


​​A message from Dr. Helena Swinkels, Office of the Chief Medical Officer

When Health Canada approved the two-dose Moderna and Pfizer-BioNTech vaccines in December 2020, a second booster dose was originally called for between 21 to 28 days after the first. However, on March 1, Provincial Health Offi​cer Dr. Bonnie Henry said the second dose can now take place after an interval of approximately 16 weeks. Why the change? 

As Dr. Henry said in a recent Zoom meeting with FNHA doctors, community Health Directors, and First Nations Chiefs, the evolving vaccination plans are “science in action.”

Since launching BC’s four-phase vaccination plan, health officials have monitored the effectiveness and safety of the vaccines. Researchers at the BC Centre for Disease Control (BCCDC) have found that the immune system builds up significant protection about 14 days after a single dose of the Pfizer and Moderna vaccines and that this protection continues to build over time. These results have been tracked among the first groups to receive vaccinations: frontline health care workers and residents of long-term care facilities, where many of the elderly vaccine recipients have multiple medical conditions. 

“A vaccine that gives 80 to 90 per cent protection in older people is the best we could hope for.” ​– Dr. Bonnie Henry 

Current research in BC and elsewhere confirms that vaccine effectiveness continues for at least two months after the first dose. And vaccine science shows that once good vaccine protection is established, immunity does not suddenly disappear but rather weakens gradually. It also shows that longer intervals between first and second doses do not compromise the booster response and in fact often produce higher antibody levels in the long term.  

All of this means that we can be confident that extending the interval between the first and second doses to 16 weeks will provide good protection to those who are vaccinated, both in the short and the long term. 

The biggest advantage from delaying second doses by 16 weeks is that it allows us to immunize more people even faster. 

In BC, the change to 16 weeks means every First Nations community in the province is on target to get first-dose immunization by the end of March. Meanwhile, urban-and-away-from-home (off-reserve) populations can expect to see their timelines moved up by as much as two months.

This doesn’t mean that this is the final word on COVID-19 vaccines. As medical science is a constant ​learning process, medical experts will continue to adapt while finding new ways to fight this infectious disease, even if it “mutates” into different variants​.

So, with evidence of continued good protection for vaccinated individuals beyond the original timelines and evidence of benefits to the population at large, BC's public health leadership made a decision that will allow the population to reach “community immunity” sooner​

The sooner we reach community immunity, the sooner we can ease public health restrictions and get back to a normal way of life. This means restoring gatherings, cultural ceremonies, and rites of passage in First Nations communities.

Until that happens, let’s keep practising public health measures, even after getting vaccinated. 

Stay informed! For the FNHA’s most up-to-date information, check FNHA COVID-19 Info.

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