Sarah Mikesell, editor with The Pig Site, spoke to Greg Page, global swine research manager with Trouw Nutrition, about immunity and vaccine use in pigs. Greg has spent the first 17 years of his career in poultry and fish nutrition and in the last three years has made the switch to leading Trouw’s global swine research team, which includes six researchers and 5 technicians who focus on executing the swine research portfolio at Trouw’s Swine Research Center in The Netherlands.
When talking about disease prevention strategies in livestock production, as an industry we are working towards a reduced reliance on the preventive use of antibiotics to ensure they remain effective for human use. This leaves producers somewhat vulnerable to increased disease pressure in their herds. However, for some diseases, vaccines have been effectively used to control/prevent disease.
Research and production of vaccines is very complex and there are some economic factors at play that may drive the decision on whether to commercialize a new vaccine or not. But let’s start at the beginning, which is why we use vaccines. The answer is because they're very effective at preventing severe disease.
One of the challenges of vaccines is that they are never 100% effective. However, they have added value in that even if they're not 100% at preventing a disease, they will mitigate the negative impacts of a disease outbreak and improve the relative survival rate. They can also help improve average daily gain (ADG) and feed conversion (FCR) among other impacts.
“The key challenge is that not all vaccines are created equal. We know from Covid-19, that we have different vaccines available. They don't all provide the same protection because the vaccines are largely composed of different types of sub-units, like mRNA vaccines and protein vaccines which all work slightly differently, but their goal is to stimulate the adaptive immune system,” said Page.
In large part, swine vaccines are fighting against live attenuated viruses, meaning they contain the live virus, although the ability to instigate full disease has been reduced significantly. They provide a little bit of a disease to prime the adaptive immune system to develop the B cells and T cells that recognize the antigens, so the host (our pig) can mount an immune response to prevent full blown disease.
“The challenge is that bacterial vaccines are based on the cellular components of the pathogen,” he said. “For example, a toxin that the pathogen produces, and the antigens don't often elicit the strongest adaptive immune response, which is why there aren't very good vaccines out there for bacterial diseases. We know E. coli, one of the biggest causes for post-weaning diarrhea in pigs, has been around for as long as pigs have been around, and even though we've been researching it for decades, we're still no closer to having a really good vaccine.”
The economic reality is that the cost of developing vaccines is extremely expensive, and, for some diseases, it will never offer the company a return on their investment. If vaccines don't provide an adequate level protection relative to the cost to develop it, no one's going to adopt it. There is also a regulatory component – it’s extremely difficult to get vaccines and other drugs approved for the livestock market, and different geographies will require different data. For example, a vaccine registered in the EU may not meet requirements for registration in the United States, Latin America or Asia, which creates a higher cost for some of these animal health companies developing the vaccines.
Because it takes a while to develop an immune response through vaccination, the window of opportunity to prevent disease may already be gone because some of these pathogens are so effective in killing their hosts.
“By the time an immune response is mounted, a producer may have already lost 50% of their herd, so that creates some challenges,” said Page. “There are new vaccines being developed for sows, and similar to what we talked about in colostrum transferring some of these immunoglobulins, they can transfer some of that passive immunity to the piglets, but some of that is transient. Other vaccines must be administered to the piglets in several doses for them to be effective.”
Looking at the Covid-19 vaccines as an example, depending on which one was administered, it may take a single dose or a double-dose vaccine, and now with the Pfizer vaccine, recipients may need a booster to extend the immunity and protection from different variants exposure.
When we apply multiple doses of vaccines to pigs, there are a host of issues that arise, such as added handling and the stress that brings to the pig in addition to the cost of multiple doses and the added labor to inject all of those animals which isn't always readily available.
“We tend to spend more time and effort vaccinating for very infectious diseases that we have good solutions that can be administered in a single dose when we are already handling the piglets, such as right after birth,” he said.
Also, he said producers may choose to spend a little bit more on the animals that are more costly, such as sows, because they have such a long productive cycle.
“There is currently an E. coli vaccine that is being trialed for sows for passive immunity transfer to the piglet,” he noted. “So, I'm holding out a lot of hope for the industry that it will be successful.”